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In this noncompliant code example, the values of objects referenced by ptr1 and ptr2 become unpredictable after the call to memcpy() because their memory areas overlap:file scope declarations assert that if an object is accessed using one of a, b, or c, and that object is modified anywhere in the program, then it is never accessed using either of the other two.

int * restrict a;
int * restrict b;

extern int c[];
 
int main(void) {
  a = c[0] = 17; 
  b = c[1] = 18;
  *a = *b; /* undefined behavior */
}

Compliant Solution

In this One compliant solution , is to simply remove the restrict-qualificatiers are removedqualification from the affected pointers. 

int * a;
int * b;

extern int c[];
 
int main(void) {
  a = c[0] = 17; 
  b = c[1] = 18;
  *a = *b; /* undefined behavior */
}

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Noncompliant Code Example

The function parameter declarad in In this noncompliant code example assert that, , the function f() accepts three parameters.  The function copies n integers from the int arrray referenced by the restrict-qualified pointer p to the int array referenced by the restrict-qualified pointer q.   Because the object is modified during each execution of the function (for which n is nonzero), if an object is accessed through one of the pointer parameters , then it is not cannot also be accessed through the other.  Declaring these function parameters as restrict-qualified pointers allows aggressive optimization by the compiler but can also result in undefined behavior if these pointers refer to overlapping objects.

void f(intsize_t n, int * restrict p, int * restrict q) {
  while (n-- > 0)
    *p++ = *q++;
}
 
void g(void) {
  extern int d[100];

  /* ... */
  f(50, d + 1, d); //* undefined behavior */
}

The function g() declares an array d consisting of 100 int values and then invokes f() to copy memory from one area of the array to another. This call has undefined behavior because each of d[1]  through d[49]  is accessed through both p  and q .

Compliant Solution

In this compliant solution, the function f() is unchanged but the programmer has ensured that none of the calls to f() result in undefined behavior.

void f(int n, int * restrict p, int * restrict q) {
   while (n-- > 0)
     *p++ = *q++; 
}
 
void g(void) {
   extern int d[100];
   f(50, d + 50, d); //  valid 
}

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